This invention relates to a circuit for calculating the RMS (Root Mean Square) value of a periodic voltage and, more particularly, to a voltage regulator for a generator which utilizes the RMS value of the voltage from the generator for regulation.
Voltage regulators for aircraft generators usually employ peak or average voltage sensing for regulation. Various specifications and military requirements, however, often list performance standards of power quantity and quality in terms of RMS values. Accordingly, regulators have been developed which sense the average or peak values of the voltage and provide RMS voltage regulation from the measured average or peak values of the voltage.
These regulators may be satisfactory for generators that provide perfect sinusoidal waveforms since a fixed relationship exists between peak or average voltages and the RMS value of the voltage. However, the output voltage from the generators is not a perfect sinusoidal waveform, and the harmonic content in the output varies between generators and with loads. The harmonic content in the output destroys the fixed relationship between the peak or average voltage and the RMS voltage. Thus, regulators that sense peak or average voltage and provide RMS voltage regulation are often inaccurate.
Several attempts have been made to more accurately provide RMS voltage regulation from regulators that sense the peak or average voltage. For example, specifically designed filters and load current feedback circuits have been designed to tailor a particular generator to a voltage regulator. Since for each application the generator and regulator has unique characteristics, a filter or feedback circuit which is designed for one may not work for another as a result of variations in the harmonic content of the output voltage from the generator.
Conventional hybrid RMS to DC converters are not capable of quickly regulating the voltage in generators because they usually include a low pass filter which introduces a lag into the information conversion process that is longer than one cycle of the frequency of the generator.